Field of the Invention
The invention relates to a device for detecting a change in a polarization direction of linearly polarized light, with a beam splitter, with which the incident linearly polarized light can be dispersed into partial beams, and with filters and detectors that are disposed behind the beam splitter in the partial beam paths.
The invention relates to a method for fabricating a device serving for detecting the polarization direction of linearly polarized light, whereby detectors are formed on a substrate, and beam splitters and filters are disposed in front of the detectors in the beam path.
Devices of this kind are primarily utilized for reading magneto-optical storage media. In magneto-optical storage media, the stored information is read by analyzing the polarization of the light that is reflected by the storage medium, because the light reflected by the storage medium is rotated xc2x15 degrees depending on the magnetization of the storage medium as a result of the Kerr effect.
For the purpose of detecting the polarization direction, there is a beam splitter in the optical path of the reflected light, which splits the incident light into two partial beams. Furthermore, discrete polarizers are disposed in the optical path of the partial beams, behind which photodiodes are disposed. Given a change of polarization direction, the signal of the photodiodes changes in characteristic fashion, so that the change of polarization direction can be deduced.
A disadvantage of the known devices is their large space requirement.
It is accordingly an object of the invention to provide a polarization detector and a method for fabricating the polarization detector that overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which detects the polarization direction of linearly polarized light and which can be integrated.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for detecting a change of a polarization direction of linearly polarized light. The device contains a beam splitter for splitting incident linearly polarized light into partial beams, and filters and detectors disposed downstream of the beam splitter in a path of the partial beams. The filters each have a first layer of a bi-refringent material for converting the incident linearly polarized light into elliptically polarized light, and a second layer of a cholesterol-phase material disposed behind the first layer in an incident direction. The filters differ with respect to a dependency of a transmission on the polarization direction of the incident linearly polarized light.
The object is inventively achieved in that the filters in the optical path of the partial beams respectively contain a first layer of a bi-refringent material, which converts the linearly polarized light into elliptically polarized light, and a second layer of a material in the cholesterol phase, which is disposed behind the first layer in the direction of incidence. The filters differ with respect to the dependency of the transmission on the polarization direction of the incident light.
In accordance with an added feature to the invention, the beam splitter is formed by a diffraction element or a hologram.
In accordance with an additional feature of the invention, the first layer contains cross-linkable polymers.
In accordance with a further feature of the invention, the first layer of each of the filters contains a xcex/4 wafer.
In accordance with another feature of the invention, the incident linearly polarized light is dispersed into two partial beams by the beam splitter.
In accordance with a further added feature of the invention, the two partial beams have an opposite helicity after passing through the xcex/4 wafer of a respective one of the filters.
It is also the object of the invention to propose a method for fabricating the device.
The object is also inventively achieved in that material for the layer in the cholesterol phase is deposited on a transparent carrier, and the carrier is attached to the substrate.
A characteristic of materials in the cholesterol phase is that they reflect light with the same helicity and pass light with the opposite helicity. If the linearly polarized light is converted into elliptically polarized light by the layer of bi-refringent material, the transmission through the layer of cholesterol-phase material depends on the alignment of the polarization vector of the incident linearly polarized light. In particular, a change of the direction of polarization is detected by way of a corresponding change of the signal level at the detectors. The inventive device thus represents a working polarization detector that is capable of detecting deviations in the polarization direction of linearly polarized light on the order of magnitude of 0.5 degrees.
The particular advantage of this is that the polarization detector according to the invention can also be built with microelectronic dimensions. In particular, the layer of cholesterol-phase material can be deposited with the aid of techniques, which are known from the semiconductor industry, for depositing photosensitive resist onto a carrier. The carrier is a transparent carrier that is placed onto the actual substrate with the photodetector. It is also possible to deposit the layer of cholesterol-phase material directly onto the substrate. The contacts formed on the substrate can then be exposed by removing the layer of cholesterol-phase material. Processes that are known in the semiconductor industry can then be applied to the fabrication of the inventive polarization detector.
With the foregoing and other objects in view there is further provided, in accordance with the invention, a method for fabricating a device for detecting a polarization direction of linearly polarized light. The method includes providing a substrate, forming detectors on the substrate, forming filters by depositing a cholesterol phase on a transparent carrier, attaching the carrier to the substrate, and disposing the filters and a beam splitter in front of the detectors in a direction of an optical path.
In accordance with an added mode of the invention, there are the steps of forming contact points in the substrate, and constructing weak points in the transparent carrier in regions that are positioned over the contact points of the substrate in a finished device.
In accordance with another mode of the invention, there is the step of removing the weak points from the transparent carrier after the transparent carrier is placed on the substrate.
In accordance with further mode of the invention, there is the step of dividing the substrate for forming individual components, after the weak points are removed.
With the foregoing and other objects in view there is additionally provided, in accordance with the invention, a method for fabricating a device for detecting a polarization direction of linearly polarized light. The method includes providing a substrate, constructing detectors on the substrate, depositing a material of a cholesterol-phase layer on the substrate, and disposing filters and a beam splitter in a direction of an optical path in front of the detectors.
In accordance with a concomitant mode of the invention, there is the step of covering the cholesterol-phase layer with a transparent carrier.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a polarization detector and a method for fabricating the polarization detector, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.